Asian languages are hard to learn because of their complex characters and pronunciations. Unlike simple languages like Spanish that can be map out word for word in English, Asian words are not easy to translate to a simple word in English. They are usually translated into sentences or phrases and vice versa, sometimes part of the meaning of the sentence can be lost when translating.
For a person learning an Asian language, constructing sentences can be really hard. The major cause of these is just the complexity of their characters and pronunciations.
The reason that Asian languages are so hard to learn is that they have unique characters and pronunctions that are unlike any other language that is around in the world today. The Asian languages are more descriptive and their words when translated into English usually come out into sentences. While some people who learn Japanese for instance could write something and a native of Japan could understand it, most likely it would not be written properly.
The Asian languages are so hard to learn because it takes so much thinking and forethought to make sure that one is speaking the language correctly. While a native speaker might be able to understand what is written or what is being spoken, most of the time it is not done correctly which in some places could be looked at as an insult. Easily put, a lot more effort needs to be put forth in order for a person to be able to master any of the Asian languages.